path: root/libjava/java/util/List.java

/* List.java -- An ordered collection which allows indexed access
   Copyright (C) 1998, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.util;

/**
 * An ordered collection (also known as a list). This collection allows
 * access to elements by position, as well as control on where elements
 * are inserted. Unlike sets, duplicate elements are permitted by this
 * general contract (if a subclass forbids duplicates, this should be
 * documented).
 * <p>
 *
 * List places additional requirements on <code>iterator</code>,
 * <code>add</code>, <code>remove</code>, <code>equals</code>, and
 * <code>hashCode</code>, in addition to requiring more methods. List
 * indexing is 0-based (like arrays), although some implementations may
 * require time proportional to the index to obtain an arbitrary element.
 * The List interface is incompatible with Set; you cannot implement both
 * simultaneously.
 * <p>
 *
 * Lists also provide a <code>ListIterator</code> which allows bidirectional
 * traversal and other features atop regular iterators. Lists can be
 * searched for arbitrary elements, and allow easy insertion and removal
 * of multiple elements in one method call.
 * <p>
 *
 * Note: While lists may contain themselves as elements, this leads to
 * undefined (usually infinite recursive) behavior for some methods like
 * hashCode or equals.
 *
 * @author Original author unknown
 * @author Eric Blake <ebb9@email.byu.edu>
 * @see Collection
 * @see Set
 * @see ArrayList
 * @see LinkedList
 * @see Vector
 * @see Arrays#asList(Object[])
 * @see Collections#nCopies(int, Object)
 * @see Collections#EMPTY_LIST
 * @see AbstractList
 * @see AbstractSequentialList
 * @since 1.2
 * @status updated to 1.4
 */
public interface List extends Collection
{
  /**
   * Insert an element into the list at a given position (optional operation).
   * This shifts all existing elements from that position to the end one
   * index to the right. This version of add has no return, since it is
   * assumed to always succeed if there is no exception.
   *
   * @param index the location to insert the item
   * @param o the object to insert
   * @throws UnsupportedOperationException if this list does not support the
   *         add operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   * @throws ClassCastException if o cannot be added to this list due to its
   *         type
   * @throws IllegalArgumentException if o cannot be added to this list for
   *         some other reason
   */
  void add(int index, Object o);

  /**
   * Add an element to the end of the list (optional operation). If the list
   * imposes restraints on what can be inserted, such as no null elements,
   * this should be documented.
   *
   * @param o the object to add
   * @return true, as defined by Collection for a modified list
   * @throws UnsupportedOperationException if this list does not support the
   *         add operation
   * @throws ClassCastException if o cannot be added to this list due to its
   *         type
   * @throws IllegalArgumentException if o cannot be added to this list for
   *         some other reason
   */
  boolean add(Object o);

  /**
   * Insert the contents of a collection into the list at a given position
   * (optional operation). Shift all elements at that position to the right
   * by the number of elements inserted. This operation is undefined if
   * this list is modified during the operation (for example, if you try
   * to insert a list into itself).
   *
   * @param index the location to insert the collection
   * @param c the collection to insert
   * @return true if the list was modified by this action, that is, if c is
   *         non-empty
   * @throws UnsupportedOperationException if this list does not support the
   *         addAll operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   * @throws ClassCastException if some element of c cannot be added to this
   *         list due to its type
   * @throws IllegalArgumentException if some element of c cannot be added
   *         to this list for some other reason
   * @throws NullPointerException if the specified collection is null
   * @see #add(int, Object)
   */
  boolean addAll(int index, Collection c);

  /**
   * Add the contents of a collection to the end of the list (optional
   * operation).  This operation is undefined if this list is modified
   * during the operation (for example, if you try to insert a list into
   * itself).
   *
   * @param c the collection to add
   * @return true if the list was modified by this action, that is, if c is
   *         non-empty
   * @throws UnsupportedOperationException if this list does not support the
   *         addAll operation
   * @throws ClassCastException if some element of c cannot be added to this
   *         list due to its type
   * @throws IllegalArgumentException if some element of c cannot be added
   *         to this list for some other reason
   * @throws NullPointerException if the specified collection is null
   * @see #add(Object)
   */
  boolean addAll(Collection c);

  /**
   * Clear the list, such that a subsequent call to isEmpty() would return
   * true (optional operation).
   *
   * @throws UnsupportedOperationException if this list does not support the
   *         clear operation
   */
  void clear();

  /**
   * Test whether this list contains a given object as one of its elements.
   * This is defined as the existence of an element e such that
   * <code>o == null ? e == null : o.equals(e)</code>.
   *
   * @param o the element to look for
   * @return true if this list contains the element
   */
  boolean contains(Object o);

  /**
   * Test whether this list contains every element in a given collection.
   *
   * @param c the collection to test for
   * @return true if for every element o in c, contains(o) would return true
   * @throws NullPointerException if the collection is null
   * @see #contains(Object)
   */
  boolean containsAll(Collection c);

  /**
   * Test whether this list is equal to another object. A List is defined to be
   * equal to an object if and only if that object is also a List, and the two
   * lists have the same sequence. Two lists l1 and l2 are equal if and only
   * if <code>l1.size() == l2.size()</code>, and for every integer n between 0
   * and <code>l1.size() - 1</code> inclusive, <code>l1.get(n) == null ?
   * l2.get(n) == null : l1.get(n).equals(l2.get(n))</code>.
   *
   * @param o the object to test for equality with this list
   * @return true if o is equal to this list
   * @see Object#equals(Object)
   * @see #hashCode()
   */
  boolean equals(Object o);

  /**
   * Get the element at a given index in this list.
   *
   * @param index the index of the element to be returned
   * @return the element at index index in this list
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   */
  Object get(int index);

  /**
   * Obtains a hash code for this list. In order to obey the general
   * contract of the hashCode method of class Object, this value is
   * calculated as follows:
   * 
<p><pre>hashCode = 1;
Iterator i = list.iterator();
while (i.hasNext())
{
  Object obj = i.next();
  hashCode = 31 * hashCode + (obj == null ? 0 : obj.hashCode());
}</pre>
   *
   * <p>This ensures that the general contract of Object.hashCode()
   * is adhered to.
   *
   * @return the hash code of this list
   * @see Object#hashCode()
   * @see #equals(Object)
   */
  int hashCode();

  /**
   * Obtain the first index at which a given object is to be found in this
   * list.
   *
   * @param o the object to search for
   * @return the least integer n such that <code>o == null ? get(n) == null :
   *         o.equals(get(n))</code>, or -1 if there is no such index
   */
  int indexOf(Object o);

  /**
   * Test whether this list is empty, that is, if size() == 0.
   *
   * @return true if this list contains no elements
   */
  boolean isEmpty();

  /**
   * Obtain an Iterator over this list, whose sequence is the list order.
   *
   * @return an Iterator over the elements of this list, in order
   */
  Iterator iterator();

  /**
   * Obtain the last index at which a given object is to be found in this
   * list.
   *
   * @return the greatest integer n such that <code>o == null ? get(n) == null
   *         : o.equals(get(n))</code>, or -1 if there is no such index
   */
  int lastIndexOf(Object o);

  /**
   * Obtain a ListIterator over this list, starting at the beginning.
   *
   * @return a ListIterator over the elements of this list, in order, starting
   *         at the beginning
   */
  ListIterator listIterator();

  /**
   * Obtain a ListIterator over this list, starting at a given position.
   * A first call to next() would return the same as get(index), and a
   * first call to previous() would return the same as get(index - 1).
   *
   * @param index the position, between 0 and size() inclusive, to begin the
   *        iteration from
   * @return a ListIterator over the elements of this list, in order, starting
   *         at index
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt; size()
   */
  ListIterator listIterator(int index);

  /**
   * Remove the element at a given position in this list (optional operation).
   * Shifts all remaining elements to the left to fill the gap.
   *
   * @param index the position within the list of the object to remove
   * @return the object that was removed
   * @throws UnsupportedOperationException if this list does not support the
   *         remove operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   */
  Object remove(int index);

  /**
   * Remove the first occurence of an object from this list (optional
   * operation). That is, remove the first element e such that
   * <code>o == null ? e == null : o.equals(e)</code>.
   *
   * @param o the object to remove
   * @return true if the list changed as a result of this call, that is, if
   *         the list contained at least one occurrence of o
   * @throws UnsupportedOperationException if this list does not support the
   *         remove operation
   */
  boolean remove(Object o);

  /**
   * Remove all elements of a given collection from this list (optional
   * operation). That is, remove every element e such that c.contains(e).
   *
   * @param c the collection to filter out
   * @return true if this list was modified as a result of this call
   * @throws UnsupportedOperationException if this list does not support the
   *         removeAll operation
   * @throws NullPointerException if the collection is null
   * @see #remove(Object)
   * @see #contains(Object)
   */
  boolean removeAll(Collection c);

  /**
   * Remove all elements of this list that are not contained in a given
   * collection (optional operation). That is, remove every element e such
   * that !c.contains(e).
   *
   * @param c the collection to retain
   * @return true if this list was modified as a result of this call
   * @throws UnsupportedOperationException if this list does not support the
   *         retainAll operation
   * @throws NullPointerException if the collection is null
   * @see #remove(Object)
   * @see #contains(Object)
   */
  boolean retainAll(Collection c);

  /**
   * Replace an element of this list with another object (optional operation).
   *
   * @param index the position within this list of the element to be replaced
   * @param o the object to replace it with
   * @return the object that was replaced
   * @throws UnsupportedOperationException if this list does not support the
   *         set operation
   * @throws IndexOutOfBoundsException if index &lt; 0 || index &gt;= size()
   * @throws ClassCastException if o cannot be added to this list due to its
   *         type
   * @throws IllegalArgumentException if o cannot be added to this list for
   *         some other reason
   */
  Object set(int index, Object o);

  /**
   * Get the number of elements in this list. If the list contains more
   * than Integer.MAX_VALUE elements, return Integer.MAX_VALUE.
   *
   * @return the number of elements in the list
   */
  int size();

  /**
   * Obtain a List view of a subsection of this list, from fromIndex
   * (inclusive) to toIndex (exclusive). If the two indices are equal, the
   * sublist is empty. The returned list should be modifiable if and only
   * if this list is modifiable. Changes to the returned list should be
   * reflected in this list. If this list is structurally modified in
   * any way other than through the returned list, the result of any subsequent
   * operations on the returned list is undefined.
   *
   * @param fromIndex the index that the returned list should start from
   *        (inclusive)
   * @param toIndex the index that the returned list should go to (exclusive)
   * @return a List backed by a subsection of this list
   * @throws IndexOutOfBoundsException if fromIndex &lt; 0
   *         || toIndex &gt; size() || fromIndex &gt; toIndex
   * @throws IllegalArgumentException if fromIndex &gt; toIndex (according to
   *         AbstractList). Don't you love Sun's inconsistent specifications?
   */
  List subList(int fromIndex, int toIndex);

  /**
   * Copy the current contents of this list into an array.
   *
   * @return an array of type Object[] and length equal to the length of this
   *         list, containing the elements currently in this list, in order
   */
  Object[] toArray();

  /**
   * Copy the current contents of this list into an array. If the array passed
   * as an argument has length less than that of this list, an array of the
   * same run-time type as a, and length equal to the length of this list, is
   * allocated using Reflection. Otherwise, a itself is used. The elements of
   * this list are copied into it, and if there is space in the array, the
   * following element is set to null. The resultant array is returned.
   * Note: The fact that the following element is set to null is only useful
   * if it is known that this list does not contain any null elements.
   *
   * @param a the array to copy this list into
   * @return an array containing the elements currently in this list, in
   *         order
   * @throws ArrayStoreException if the type of any element of the
   *         collection is not a subtype of the element type of a
   * @throws NullPointerException if the specified array is null
   */
  Object[] toArray(Object[] a);
}